Pump

ABSTRACT

There is disclosed a pump comprising a pump housing, an impeller, and a motor. The pump housing comprises a pump chamber and at least one communication port opening into this pump chamber. The impeller comprises a plurality of vanes and is rotatably disposed in the pump chamber. The motor has a plurality of phases, and rotates the impeller. The number of communication ports, the number of vanes, and the number of phases of the motor are set in such a manner as to indicate prime numbers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2004-163407, filed Jun. 1, 2004, the entire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

The present invention relates to a pump for use in feeding out a fluid.

2. Description of the Related Art

A central processing unit (CPU) for use in an electronic apparatus has a tendency wherein a heating amount during operation increases with raised processing speed or increased functions. As a countermeasure against this heat, in recent years, an electronic apparatus has been put to practical use, comprising a so-called liquid cooling system cooling device which cools the CPU using a liquid refrigerant having a specific heat much higher than that of air.

As a cooling device, as described in Japanese Patent No. 3452059, a device having a heat exchange type pump has been proposed. A contact heat exchange type pump closely adheres to a heating electronic component such as a CPU, the heating electronic component exchanges heat with the liquid refrigerant to thereby cool the heating electronic component, and further the liquid refrigerant is circulated.

As the pump applied to the cooling device, sound produced at a driving time has been required to be excessively reduced.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a perspective view showing a portable computer comprising a cooling device having a pump according to a first embodiment of the present invention;

FIG. 2 is a partially sectional side view of the portable computer of FIG. 1;

FIG. 3 is a bottom plan view of the portable computer of FIG. 1;

FIG. 4 is a partially sectional plan view of the portable computer of FIG. 1 in a state in which the cooling device is contained in a first housing;

FIG. 5 is an exploded perspective view of the pump;

FIG. 6 is a plan view of the pump as viewed from a heat receiving plate side;

FIG. 7 is a plan view of the pump as viewed from a bottom side in a state in which the heat receiving plate is omitted;

FIG. 8 is a sectional view of FIG. 7 cut along a line VIII-VIII;

FIG. 9 is a diagram showing a relation between vane rotation frequency and sound pressure level in a case where the number of communication ports which open into a pump chamber, the number of vanes of an impeller, and motor phase number have a common divisor other than 1; and

FIG. 10 is a plan view showing a pump according to a second embodiment of the present invention as viewed from a bottom side in a state in which a heat receiving plate is omitted.

DETAILED DESCRIPTION

A first embodiment of the present invention will be described hereinafter with reference to FIGS. 1 to 8. In the present embodiment, a pump of the present invention will be described in accordance with one example applied to a cooling device disposed in a portable computer which is an electronic apparatus.

FIGS. 1 to 3 show a portable computer 1 which is the electronic apparatus. The portable computer 1 comprises a main unit 2 and a display unit 3. The main unit 2 comprises a first housing 10 having a flat box shape. The first housing 10 comprises a bottom wall 11 a, an upper wall 11 b, a front wall 11 c, right and left side walls 11 e, 11 d, and a rear wall 11 f. The upper wall 11 b supports a keyboard 12.

As shown in FIG. 2, at least the bottom wall 11 a of the first housing 10 is formed, for example, of a metal material such as a magnesium alloy. The bottom wall 11 a has a protruding portion 13 and a concave portion 14. The protruding portion 13 is positioned in a rear half portion of the bottom wall 11 a, and protrudes downwards from a front half portion of the bottom wall 11 a. The concave portion 14 is recessed toward the inside of the first housing 10 immediately before the protruding portion 13. The concave portion 14 is positioned in a middle portion along a width direction of the first housing 10.

As shown in FIGS. 2 and 3, a pair of first leg portions 15 a, 15 b (only one is shown in FIG. 2) are formed in the bottom of the protruding portion 13. These leg portions 15 a, 15 b are disposed apart from each other in a width direction of the first housing 10. Similarly, a pair of second leg portions 16 a, 16 b (only one is shown in FIG. 2) are formed on a front end portion of the bottom wall 11 a. These second leg portions 16 a, 16 b are disposed apart from each other in the width direction of the first housing 10.

The first and second leg portions 15 a, 15 b, 16 a, 16 b contact the upper surface of a top plate B. As a result, the first housing 10 tilts in a front downward posture, and a gap S is formed between the bottom of the protruding portion 13 and the upper surface of the top plate B.

As shown in FIGS. 2 and 3, the rear wall 11 f of the first housing 10 has a plurality of first exhaust ports 17. The first exhaust ports 17 are arranged in a row in the width direction of the first housing 10. As shown in FIG. 3, the protruding portion 13 has a partition wall 18 interposed between the protruding portion and the concave portion 14. A plurality of second exhaust ports 19 are formed in this partition wall 18. The second exhaust ports 19 are arranged in one row in the width direction of the first housing 10, and opened in the concave portion 14.

As shown in FIG. 1, the display unit 3 comprises a second housing 20 and a liquid crystal display panel 21. The liquid crystal display panel 21 is contained in the second housing 20. The liquid crystal display panel 21 has a screen 21 a which displays an image. The screen 21 a is exposed to the outside of the second housing 20 through an opening 22 formed in the front surface of the second housing 20.

The second housing 20 is supported on a rear end portion of the first housing 10 via a hinge (not shown). Therefore, the display unit 3 between a closed position in which the unit is laid on the main unit 2 in such a manner as to cover the keyboard 12 from above and an opened position in which the unit rises with respect to the main unit 2 in such a manner as to expose the keyboard 12 or the screen 21 a.

As shown in FIGS. 2, 4, and 8, the first housing 10 contains a printed circuit board 30. A CPU 31 which is a heating member is mounted on the upper surface of the rear end portion of the printed circuit board 30. As shown in FIG. 8, the CPU 31 has a base substrate 32, and an IC chip 33 positioned in a middle portion of the upper surface of a base substrate 32. The IC chip 33 has a very large heating amount during operation with raised processing speed or increased functions, and cooling is required for maintaining stable operation.

As shown in FIG. 4, a liquid cooling system cooling device 40 which cools the CPU 31 using a liquid refrigerant such as an antifreezing solution is mounted on the portable computer 1. The cooling device 40 is contained in the first housing 10. The cooling device 40 comprises a pump 41 functioning both as a heat receiving portion and a heat exchanger, a radiator 42 which is a heat emitting portion, a circulation path 43 and the like.

As shown in FIGS. 4 to 8, the pump 41 forcibly circulates the liquid refrigerant in the circulation path 43, and comprises a pump housing 50 which also functions as the heat receiving portion, an impeller 70, a motor 80 (see FIG. 8) and the like.

The pump housing 50 has a flat box shape which is one size larger than the CPU 31 and whose flat face is substantially square. As shown in FIG. 5, the pump housing 50 comprises, for example, a housing main body 51 and a heat receiving plate 53 which is a heat receiving portion. The housing main body 51 is formed, for example, of a synthetic resin. It is to be noted that the housing main body 51 may be formed of a metal material superior in thermal conductivity, such as an aluminum alloy. The housing main body 51 has a concave portion 52 opened downwards. The heat receiving plate 53 functions as a cover of the housing main body 51. The heat receiving plate 53 is disposed on the housing main body 51 in such a manner as to cover an opening end of the concave portion 52. The lower surface of the heat receiving plate 53 constitutes a flat heat receiving face 54. The heat receiving plate 53 is formed of a metal material superior in thermal conductivity, such as copper and aluminum alloy, and closes the opening end of the concave portion 52 in a liquid-tight manner via an O-ring 55.

As shown in FIGS. 5, 7, and 8, the inside of the pump housing 50 is partitioned into a pump chamber 57 and a reserve tank 58 by a partition wall 56. As shown in FIG. 4, the pump chamber 57 is disposed toward one corner portion C1 among four corner portions C1 to C4 of the housing main body 51. The reserve tank 58 stores the liquid refrigerant, and surrounds the pump chamber 57. The partition wall 56 rises from an upper wall 51 a of the housing main body 51. In the partition wall 56, at least one communication port is formed which opens into the pump chamber 57, that is, which connects the pump chamber 57 to the reserve tank 58. The number of communication ports is set to be a prime number. In this pump housing 50, two communication ports including a first communication port 59 and a second communication port 60 are disposed in the partition wall 56.

The corner portion C3 positioned diagonally to the corner portion C1 is cut among four corner portions C1 to C4 of the housing main body 51. This corner portion C3 is provided with a discharge tube 61 as a first communication portion which connects the inside of the pump housing 50 to the outside of the pump housing 50, and a suction tube 62 as a second communication portion which connects the inside of the pump housing 50 to the outside of the pump housing 50. The discharge tube 61 and the suction tube 62 are disposed horizontally at an interval therebetween. An upstream end of the discharge tube 61 and a downstream end of the suction tube 62 protrude to the outside via the housing main body 51.

A first communication tube 63 is disposed between the upstream end of the discharge tube 61 and the first communication port 59 disposed in the partition wall 56. A second communication tube 64 is disposed between the downstream end of the suction tube 62 and the second communication port 60 disposed in the partition wall 56. The first communication tube 63 and the second communication tube 64 are formed into a unit to constitute a communication tube unit 65.

That is, the upstream end of the discharge tube 61 communicates with the pump chamber 57 via the first communication tube 63 and the first communication port 59. The downstream end of the suction tube 62 communicates with the pump chamber 57 via the second communication tube 64 and the second communication port 60. It is to be noted that a hole 66 for gas/liquid separation may be disposed in the first communication tube 63 or the second communication tube 64. In this case, even when orientation of the pump housing 50 is changed in any direction, the position of the hole 66 is preferably set in such a manner as to be constantly under a liquid surface of the liquid refrigerant stored in the reserve tank 58.

Moreover, the outer surface (upper surface of the pump housing 50) of the upper wall 51 a of the housing main body 51 has a stator containing concave portion (see FIG. 8) 67 which contains a stator 82 described later, and a control substrate containing concave portion (not shown) which contains a control substrate (not shown). As shown in FIG. 8, in the housing main body 51, a cover 50 a may be disposed which covers the stator 82 and the control substrate and which inhibits leakage or evaporation of the liquid refrigerant contained in the pump housing 50.

The disc-shaped impeller 70 is contained in the pump chamber 57 of the pump housing 50. The impeller 70 stirs the liquid refrigerant in the pump chamber 57, and feeds out the liquid refrigerant to the outside (circulation path 43) of the pump housing 50 from the pump housing 50. The impeller 70 is formed, for example, of a resin, and has a disc-shaped main body portion 71, a rotation shaft 72 passing through the center of the main body portion 71, and a plurality of vanes 73 disposed on at least one end face among a pair of end faces of the main body portion 71, for example, the end face facing the heat receiving plate 53. The number of vanes 73 of the impeller 70 is set in such a manner as to be a prime number. This impeller 70 has, for example, seventeen vanes 73. As shown in FIGS. 5 and 7, these vanes 73 are radially arranged with respect to the center of rotation (rotation shaft 72) of the impeller 70. The vanes 73 are arranged at an equal interval in such a manner that the angle θ1 formed by each pair of adjacent vanes 73 is constant (the equal angle). As shown in FIG. 8, the impeller 70 is rotatably supported by the upper wall 51 a of the housing main body 51 and the heat receiving plate 53 in such a posture that the rotation shaft 72 extends over the upper wall 51 a of the housing main body 51 and the heat receiving plate 53.

As shown in FIG. 8, the motor 80 which rotates the impeller 70 is incorporated in the pump housing 50. The motor 80 has a plurality of phases. As the motor 80, for example, there is an induction motor having a rotor 81 and a stator 82. The rotor 81 has a ring shape. The rotor 81 is coaxially fixed to the main body portion 71 of the impeller 70, and contained in the pump chamber 57. A rotor magnet 81 a in which a plurality of cathodes and anodes are alternately magnetized is fitted in the rotor 81. The rotor magnet 81 a rotates integrally with the rotor 81 and the impeller 70. The stator 82 has a plurality of magnetic poles as a plurality of phases. This stator 82 has a plurality of coils 83, for example, as a plurality of phases. The number (corresponding to the number (pole number) of the coils 83 in the present embodiment) of phases of the motor 80 is set in such a manner as to be a prime number. As shown in FIG. 5, the stator 82 has, for example, seven coils 83.

As shown in FIG. 8, the stator 82 is contained in the stator containing concave portion 67 owned by the outer surface of the upper wall 51 a of the housing main body 51. The stator containing concave portion 67 enters the rotor 81. Therefore, the stator 82 is coaxially contained in the rotor 81. The control substrate is contained in the control substrate containing concave portion, and is electrically connected to the stator 82.

Power conduction to the stator 82 is performed simultaneously, for example, with turning-on of a power supply of the portable computer 1. By the power conduction, a rotary magnetic field is generated in a peripheral direction of the stator 82, and this magnetic field is magnetically bonded to the magnet of the rotor 81. As a result, a torque along the peripheral direction of the rotor 81 is generated between the stator 82 and the rotor magnet 81 a of the rotor 81, and the impeller 70 rotates in a clockwise direction.

As described above, the lower surface of the heat receiving plate 53 has a flat heat receiving face 54. On the other hand, as shown in FIGS. 6 and 8, a convex portion 90 which is referred to as so-called side channel is disposed in a position facing the pump chamber 57 on the upper surface of the heat receiving plate 53.

An end face 91 of the convex portion 90 has: a part (circular arc) 92 of a circle concentric to a rotation center O (rotation center O of the impeller 70 is on a central axis line L (see FIG. 8) of the rotation shaft 72 of the impeller 70) of the impeller 70; a pair of edges 93 a, 93 b extending radially with respect to a center (position facing the rotation center O of the impeller 70) of the circular arc 92 from opposite ends of a part of the circular arc 92; and a circular arc 94 connecting tip ends of these edges 93 a, 93 b to each other. The end face is formed substantially in a fan shape. The convex portion 90 is disposed on the upper surface of the heat receiving plate 53 in such a manner that the circular arc 94 faces the communication ports 59, 60 of the partition wall 56. It is to be noted that the convex portion 90 may be formed integrally with or separately from the heat receiving plate 53.

The convex portion 90 satisfactorily feeds the liquid refrigerant which is taken into the pump chamber 57 from the second communication port 60 and which is passed in a peripheral direction in the pump chamber 57 by the impeller 70 to the outside of the pump chamber 57 from the first communication port 59. That is, since the convex portion 90 is disposed, a part of the liquid refrigerant stirred in the pump chamber 57 abuts the side surface of the convex portion 90, rides on the convex portion 90, and changes its circulation direction toward the first communication port 59. Therefore, the liquid refrigerant stirred in the pump chamber 57 can be satisfactorily fed to the outside of the pump chamber 57 from the first communication port 59.

As shown in FIG. 7, assuming that an angles formed by each pair of the adjacent vanes 73 is θ1, and an angle formed by a pair of edges 93 a, 93 b of the end face 91 of the convex portion 90 is θ2 in the pump 41, these angles θ1 and θ2 are set such that the value of θ2/θ1 is not an integer. The quotient (value of θ2/θ1) obtained by dividing θ1 by θ2 may be an irrational number.

Additionally, sound produced in driving the above-described pump 41 is divided into a periodic sound and an a periodic sound. For example, there are the following periodic sounds:

-   -   (1) sound which is produced at a time when a pressure         fluctuation is generated in the liquid refrigerant with the         rotation of the impeller 70 and which is determined by the         number of vanes 73 of the impeller 70 and a rotation number of         the impeller 70;     -   (2) sound produced by the pressure fluctuation generated in the         liquid refrigerant, when the vanes 73 of the impeller 70 pass         through the communication ports 59, 60 opened in the pump         chamber 57;     -   (3) sound produced by the number determined by a product of the         phase number of the motor 80 and the rotation number of the         impeller 70, where the number determined by the phase number of         the motor 80 is a multiple number of a product of the phase         number (the number of coils 83 in the motor 80) of the stator 82         and the phase number (pole number of the rotor magnet 81 a in         the motor 80) of the rotor 81; and     -   (4) sound produced by the pressure fluctuation produced in the         liquid refrigerant, when the vanes 73 of the impeller 70 pass         through the convex portion 90.

As shown in FIG. 9, the periodic sound as in the above (1) is periodically produced as one-time wave (n=1), two-time wave (n=2), three-time wave (n=3) . . . in accordance with the following equation (5): (the number of vanes 73 of the impeller 70×frequency of the rotation of the impeller 70)×n (n is a natural number)   (5).

Therefore, the periodic sound produced by the pump 41 increases in a case where a value overlaps with a peak value of a sound pressure level developed in the above equation (5). For example, the followings are cases where the peak value of the sound pressure level produced by the above equation (5) overlaps with that of the sound pressure level of another periodic sound:

-   -   (2′) the number of vanes 73 of the impeller 70 and communication         ports 59, 60 opened in the pump chamber 57 have a common         divisor;     -   (3′) the number of vanes 73 of the impeller 70 and the phase         number (number of coils 83 of the stator 82 in the motor 80) of         the motor 80 have a common divisor; and     -   (4′) θ2/θ1 is an integer, assuming that the angle formed by each         pair of the adjacent vanes 73 is θ1, and the angle formed by a         pair of edges of the end face 91 of the convex portion 90 is θ2.

Therefore, in the pump 41, the number of communication ports 59, 60, the number of vanes 73, and the number of coils 83 of the stator 82 which is the phase number of the motor 80 are all prime numbers. As shown in FIG. 5, in the pump 41, for example, the number of communication ports 59, 60 is set to two, the number of vanes 73 is set to 17, and the number of coils 83 is set to seven.

It is to be noted that as a combination of the number of communication ports, the number of vanes, and the phase number of the motor, the number of communication ports is preferably set to two, the number of vanes is set to 23, and the motor is set to three poles.

In this case, the peak value of the sound pressure level of the sound produced by the pressure fluctuation of the liquid refrigerant when the impeller 70 rotates, the peak value of the sound pressure level of the sound produced by the pressure fluctuation in the liquid refrigerant when the vanes 73 of the impeller 70 pass through the communication ports 59, 60 opened in the pump chamber 57, and the peak value of the sound pressure level of the sound produced by the product of the number determined by the phase number of the motor 80 and the rotation number of the impeller 70 do not easily overlap. Therefore, the sound produced at a driving time of the pump 41 can be reduced.

Moreover, as shown in FIG. 7, assuming that the angle formed by each pair of the adjacent vanes 73 is θ1, and the angle formed by one pair of edges of the end face 91 of the convex portion 90 is θ2, the value of θ2/θ1 is not an integer. In the present embodiment, the value of θ2/θ1 is set to an irrational number.

Therefore, a timing at which the first communication port 59 and the vanes 73 of the impeller 70 pass each other, and a timing at which the second communication port 60 and the vanes 73 of the impeller 70 pass each other can be displaced. Therefore, the sound produced at the driving time of the pump 41 can be reduced.

In the pump 41 constituted in this manner, for example, the CPU 31 is laid on the printed circuit board 30 in such a manner as to cover the CPU 31 from above in a state in which the center of the pump housing 50 is matched with that (the same center as that of the IC chip 33) of the CPU 31. It is to be noted that the matching of the center of the pump housing 50 with that of the CPU 31 means that a perpendicular line passing through the center of the pump housing 50 passes through the center of the CPU 31.

As shown in FIG. 8, the pump housing 50 of the pump 41 is fixed to the bottom wall 11 a of the first housing 10 together with the printed circuit board 30. As shown in FIG. 4, the pump housing 50 has three attaching portions 68 a, 68 b, 68 c in two adjacent corner portions among four corner portions C1 to C4, for example, in the corner portions C1, C2 and a middle portion of two remaining corner portions C3, C4. The bottom wall 11 a of the first housing 10 has three boss portions 34 in positions corresponding to the three attaching portions 68 a, 68 b, 68 c.

The boss portions 34 protrude upwards from the bottom wall 11 a. The printed circuit board 30 is superimposed upon the tip surfaces of the boss portions 34.

In addition to the above-described attaching portions 68 a, 68 b, 68 c, an attaching mechanism for attaching the pump 41 to the first housing 10 comprises three cylindrical inserts 100, three coil springs 101, three C-rings 102, three screws 103 and the like. Each insert 100 has a protruding portion 100 a protruding to the outside in a horizontal direction along a peripheral direction in an upper end.

The pump 41 is fixed in a pressed state with respect to the CPU 31 as follows. It is to be noted that FIG. 8 shows an only attaching structure in the attaching portion 68 a, and the pump is also attached to the attaching portions 68 b, 68 c in a similar structure.

First, the inserts 100 are passed through the coil springs 101. The insert 100 is inserted into the attaching portion 68 a. The C-ring 102 for preventing falling is fitted in the insert 100. Accordingly, the insert 100 is in an urged state in a direction in which the protruding portion 100 a is detached from the heat receiving plate 53 by the coil spring 101.

A thermally conductive grease (not shown) is applied to either the upper surface of the IC chip 33 or a region facing the IC chip 33 of the heat receiving face 54, and the heat receiving face 54 of the pump housing 50 is disposed facing the IC chip 33. The screws 103 are passed through the inserts 100, and screwed into the boss portions 34 on the printed circuit board 30. Accordingly, the inserts 100 are fixed to the boss portions 34, and the pump 41 is pressed onto the IC chip 33 by elastic properties of the coil springs 101. Consequently, the IC chip 33 is thermally connected to the heat receiving face 54 of the pump housing 50 via the conductive grease.

As shown in FIG. 2, the radiator 42 of the cooling device 40 is contained in the protruding portion 13 of the first housing 10. The radiator 42 comprises a fan 131 and a heat emitting member 132. The fan 131 has a flat case 133, and a centrifugal impeller 134 contained in the case 133.

The impeller 134 has a rotation center 134 a, and a plurality of vanes 134 b protruding radially from the rotation center. The impeller 134 is supported by the case 133 via a flat motor (not shown). In this motor, the impeller 134 is rotated in a counterclockwise direction as shown by arrows in FIG. 4.

The heat emitting member 132 of the radiator 42 comprises a refrigerant passage 112 through which the liquid refrigerant flows and a plurality of heat emitting fins 113. The refrigerant passage 112 comprises, for example, a flat copper pipe, and has long and short axes. The refrigerant passage 112 has an annular shape which coaxially surrounds the impeller 134. This refrigerant passage 112 is superimposed upon the bottom of the protruding portion 13 in a posture of the short axis along the thickness direction of the first housing 10. Therefore, the refrigerant passage 112 is thermally connected to the first housing 10. The refrigerant passage 112 has an upstream end 114 and a downstream end 115. The upstream end 114 constitutes a refrigerant inlet 114 a into which the liquid refrigerant flows, and the downstream end 115 constitutes a refrigerant outlet 115 a from which the liquid refrigerant flows. The refrigerant passage 112, upstream end 114, and downstream end 115 form a part of the circulation path 43 (the circulation path 43 will be described later in detail).

Each heat emitting fin 113 is formed of a metal material superior in thermal conductivity, such as an aluminum alloy, and has a square plate shape. The heat emitting fins 113 are arranged at intervals in the peripheral direction of the impeller 134, and are radially arranged with respect to the impeller 134.

The heat emitting fins 113 rise along the thickness direction of the first housing 10. A lower end of the heat emitting fin 113 is fixed to the upper surface of the flat refrigerant passage 112 by means such as soldering. Accordingly, the arrangement intervals of the heat emitting fins 113 are determined, and the heat emitting fins 113 are thermally connected to the refrigerant passage 112. The upper ends of the heat emitting fins 113 abut the inner surface of the upper wall of the case 133, and are thermally connected to the case 133.

The circulation path 43 of the cooling device 40 has a first pipeline 121 and a second pipeline 122. The first pipeline 121 connects the discharge tube 61 of the pump housing 50 to the refrigerant inlet 114 a of the refrigerant passage 112. The second pipeline 122 connects the suction tube 62 of the pump housing 50 to the refrigerant outlet 115 a of the refrigerant passage 112.

In other words, the refrigerant passage 112 of the heat emitting member 132 functions as a third pipeline which connects the first pipeline 121 to the second pipeline 122. As a result, the liquid refrigerant circulates between a pump unit 25 and the radiator 42 through the first pipeline 121, the second pipeline 122, and the refrigerant passage 112.

Next, an operation of the cooling device 40 will be described.

The IC chip 33 of the CPU 31 generates heat during use of the portable computer 1. The heat emitted by the IC chip 33 is conducted to the pump housing 50 through the heat receiving face 54. Since the pump chamber 57 and the reserve tank 58 of the pump housing 50 are filled with the liquid refrigerant, the liquid refrigerant absorbs much of the heat conducted to the pump housing 50.

The power conduction to the stator 82 of the motor 80 is performed simultaneously with the turning-on of the power supply to the portable computer 1. Accordingly, a torque is generated between the stator 82 and the rotor magnet 81 a of the rotor 81, and the rotor 81 rotates together with the impeller 70. When the impeller 70 rotates, the liquid refrigerant in the pump chamber 57 is pressurized and discharged from the discharge tube 61, and guided to the radiator 42 through the first pipeline 121.

In the pump 41, the number of communication ports 59, 60, the number of vanes 73, and the phase number (the number of coils 83 of the stator 82) of the motor 80 are set in such a manner as to be all prime numbers. Therefore, the peak value of the sound pressure level of the sound produced by the pressure fluctuation in the liquid refrigerant when the vanes 73 of the impeller 70 pass through the communication ports 59, 60 opened in the pump chamber 57, the peak value of the sound pressure level of the sound produced by the product of the number determined by the phase number of the motor 80 and the rotation number of the impeller 70, and the peak value of the sound pressure level produced by the pressure fluctuation in the liquid refrigerant when the impeller 70 rotates do not easily overlap. In the pump 41, assuming that the angle formed by each pair of adjacent vanes 73 is θ1, and the angle formed by one pair of the edges of the end face 91 of the convex portion 90 is θ2, these angles θ1 and θ2 are set in such a manner that θ2/θ1 is not an integer. Therefore, the timing at which the first communication port 59 and the vanes 73 of the impeller 70 pass each other, and the timing at which the second communication port 60 and the vanes 73 of the impeller 70 pass each other are displaced. Therefore, the sound produced at the driving time of the pump 41 is less than before.

The liquid refrigerant heated by heat exchange in the pump housing 50 is fed into the refrigerant passage 112 from the refrigerant inlet 114 a. The liquid refrigerant flows toward the refrigerant outlet 115 a in the refrigerant passage 112. In a flow process, the heat of the IC chip 33 absorbed by the liquid refrigerant is conducted to the refrigerant passage 112, and is further conducted to the heat emitting fins 113 from the refrigerant passage 112.

According to the present embodiment, since the refrigerant passage 112 is thermally connected to the protruding portion 13 of the first housing 10, the heat conducted to the refrigerant passage 112 from the liquid refrigerant can be diffused in the first housing 10. Moreover, since the heat emitting fins 113 are thermally connected to the upper wall of the case 133, the heat conducted to the heat emitting fins 113 from the liquid refrigerant can be released to the case 133.

When the impeller 134 of the radiator 42 rotates during the use of the portable computer 1, air is discharged radially from an outer peripheral portion of the impeller 134. The air passes through the adjacent heat emitting fins 113 as cooling air. Accordingly, the refrigerant passage 112 and the heat emitting fins 113 are cooled, and most of the heat conducted to both is taken away with the flow of cooling air. Moreover, this cooling air is discharged to the rear part of the first housing 10 via the first and second exhaust ports 17, 19 of the first housing 10 together with the heat. At this time, the second exhaust ports 19 are opened in the concave portion 14 of the bottom wall 11 a. Moreover, when the portable computer 1 is laid on the top plate B of a desk, a gap S connected to the concave portion 14 is formed between the bottom wall 11 a and the top plate B. Therefore, the cooling air discharged from the second exhaust ports 19 is discharged to the outside of the first housing 10 from the concave portion 14 via the gap S, and the flow of cooling air is not inhibited by the top plate B.

In contrast, the liquid refrigerant cooled by the heat exchange in the radiator 42 is guided into the suction tube 62 of the pump housing 50 from the refrigerant outlet 115 a via the second pipeline 122. This liquid refrigerant is discharged to the inside of the pump housing 50 from the downstream end of the suction tube 62 through the second communication port 60.

The liquid refrigerant returned to the pump housing 50 is sucked into the pump chamber 57 from the communication port 60. The liquid refrigerant sucked into the pump chamber 57 is pressurized again and fed into the radiator 42 from the discharge tube 61.

When this cycle is repeated, the heat of the IC chip 33 is successively transferred to the heat emitting member 132 of the radiator 42, flows on the flow of cooling air passing among the heat emitting fins 113 of the heat emitting member 132, and is discharged to the outside of the portable computer 1.

As described above, according to the pump 41 of the present embodiment, the number of communication ports 59, 60, the number of vanes 73 of the impeller 70, and the phase number of the motor 80 are set in such a manner as to be all prime numbers. Therefore, the peak value of the sound pressure level of the sound produced by the pressure fluctuation in the liquid refrigerant when the vanes 73 of the impeller 70 pass through the communication ports 59, 60 opened in the pump chamber 57, the peak value of the sound pressure level of the sound produced by the product of the number determined by the phase number of the motor 80 and the rotation number of the impeller 70, and the peak value of the sound pressure level produced by the pressure fluctuation in the liquid refrigerant when the impeller 70 rotates do not easily overlap. Therefore, the sound produced at the driving time of the pump 41 can be reduced.

Moreover, according to the pump 41 of the present embodiment, assuming that the angle formed by the adjacent vanes 73 is θ1, and the angle formed by one pair of the edges 93 a, 93 b of the end face 91 of the convex portion 90 is θ2, these angles θ1 and θ2 are set in such a manner that θ2/θ1 is not an integer (the irrational number is achieved in the present embodiment). Therefore, the timing at which the first communication port 59 and the vanes 73 of the impeller 70 pass each other, and the timing at which the second communication port 60 and the vanes 73 of the impeller 70 pass each other are displaced. Therefore, the sound produced at the driving time of the pump 41 can be reduced.

Furthermore, in the pump 41 of the present embodiment, the pump housing 50 has the heat receiving face 54 thermally connected to the CPU 31 which is a heat emitting member. Therefore, this pump 41 functions not only as the heat exchanger which feeds out a fluid such as a liquid refrigerant but also as the heat receiving portion which receives the heat of a heating member such as a CPU 31. Additionally, the sound produced at the driving time of the pump 41 is small. Therefore, the pump can be preferably used in the liquid-cooling system cooling device 40 mounted on the electronic apparatus, for example, the portable computer 1.

A second embodiment of the present invention will be described with reference to FIG. 10.

In a pump 41 of the present embodiment, the number of vanes 73 of an impeller 70 is set to a prime number, for example, 17. The vanes 73 are arranged in unequal intervals in such a manner that at least one of angles formed by each pair of adjacent vanes 73 has a different from the other said angles. The vanes 73 are arranged at unequal intervals in such a manner that the adjacent vanes 73 form different angles. At this time, preferably a value obtained by dividing an angle θ2 formed by a pair of edges 93 a, 93 b of an end face 91 of a convex portion 90 by an angle formed by the each pair of adjacent vanes 73 is not an integer.

It is to be noted that when the vanes 73 are arranged at unequal intervals (non-constant intervals), the number of vanes 73 does not necessarily have to be a prime number. Since another constitution is the same as that of the first embodiment including portions (not shown), the constitution is denoted with the same reference numerals, and redundant description is omitted.

According to the pump 41 of the present embodiment, the vanes 73 are arranged at unequal intervals (non-constant intervals) in such a manner that at least one of the angles formed by the each pair of adjacent vanes 73 is different from the other said angles. In this case, when the impeller 70 rotates, the timing at which the individual vanes 73 impart pressure changes to the liquid refrigerant can be displaced. The timing at which the first communication port 59 and the vanes 73 of the impeller 70 pass each other, and the timing at which the second communication port 60 and the vanes 73 of the impeller 70 pass each other can be displaced. Therefore, the sound produced at the driving time of the pump 41 can be reduced.

It is to be noted that the pump of the present invention can be used broadly not only in an electronic apparatus such as a portable computer but also in a cooling device mounted on the electronic apparatus, and another apparatus. 

1. A pump comprising: a pump housing having a pump chamber and at least one communication port opening into this pump chamber; an impeller having a plurality of vanes and being rotatably disposed in the pump chamber; and a motor having a plurality of phases and rotating the impeller, wherein the number of communication ports, the number of vanes, and the number of phases of the motor are prime numbers.
 2. The pump according to claim 1, wherein the plurality of vanes are arranged radially with respect to the center of rotation of the impeller, and the plurality of vanes are arranged at equal intervals in such a manner that the angle formed by each pair of adjacent vanes is constant.
 3. The pump according to claim 2, wherein the pump housing has a pair of faces which define the pump chamber, a convex portion including an end face having a pair of edges extending radially from a position facing the center of rotation of the impeller is disposed on at least one face of the pair of faces, and, assuming that the angle formed by each pair of adjacent vanes is θ1, and the angle formed by the pair of edges of the end face of the convex portion is θ2, the angles θ1 and θ2 are set such that the value of θ2/θ1 is not an integer.
 4. The pump according to claim 3, wherein, assuming that the angle formed by each pair of adjacent vanes is θ1, and the angle formed by the pair of edges of the end face of the convex portion is θ2, the angles θ1 and θ2 are set such that the value of θ2/θ1 is an irrational number.
 5. The pump according to claim 1, wherein the plurality of vanes are arranged radially with respect to the center of rotation of the impeller, and the plurality of vanes are arranged at unequal intervals such that at least one of the angles formed by each pair of adjacent vanes is different from the other said angles.
 6. The pump according to claim 1, wherein the pump housing has a heat receiving face thermally connected to a heat emitting member.
 7. A pump comprising: a pump housing having a pump chamber and at least one communication port opening into this pump chamber; an impeller comprising a plurality of vanes and being rotatably disposed in the pump chamber; an annular rotor magnet disposed in the impeller; and a stator having a plurality of phases and being disposed inside the rotor magnet, wherein the number of communication ports, the number of vanes, and the number of phases of the stator are prime numbers.
 8. The pump according to claim 7, wherein the plurality of vanes are arranged radially with respect to the center of rotation of the impeller, and the plurality of vanes are arranged at equal intervals in such a manner that the angle formed by each pair of adjacent vanes is constant.
 9. The pump according to claim 8, wherein the pump housing has a pair of faces which define the pump chamber, a convex portion including an end face having a pair of edges extending radially from a position facing the center of rotation of the impeller is disposed on at least one face of the pair of faces, and, assuming that the angle formed by each pair of adjacent vanes is θ1, and the angle formed by the pair of edges of the end face of the convex portion is θ2, the angles θ1 and θ2 are set such that the value of θ2/θ1 is not an integer.
 10. The pump according to claim 9, wherein, assuming that the angle formed by each pair of adjacent vanes is θ1, and the angle formed by the pair of edges of the end face of the convex portion is θ2, the angles θ1 and θ2 are set such that the value of θ2/θ1 is an irrational number.
 11. The pump according to claim 7, wherein the plurality of vanes are arranged radially with respect to the center of rotation of the impeller, and the plurality of vanes are arranged at unequal intervals such that at least one of the angles formed by each pair of adjacent vanes is different from the other said angles.
 12. The pump according to claim 7,wherein the pump housing has a heat receiving face thermally connected to a heat emitting member.
 13. A pump comprising: a pump housing comprising a pump chamber; an impeller comprising a plurality of vanes and being rotatably disposed in the pump chamber; and a motor which rotates the impeller, wherein the plurality of vanes are arranged radially with respect to the center of rotation of the impeller, and in such a manner that the angles formed by each pair of adjacent vanes represent non-constant interval.
 14. The pump according to claim 13,wherein the pump housing has a heat receiving face thermally connected to a heat emitting member. 